This invention relates to an electrical door operator which is adapted for preferred use in buildings or other stationary structures to drive a relatively large door between open and closed positions. More particularly, this invention relates to a door operator incorporating a stationary dual-phase linear induction motor, and wherein the linear movement of the armature of the motor is adapted to control the movement of a door member in a building such as a garage, warehouse, or the like.
Heretofore, electrically powered door openers, and especially those suitable for operation in combination with a segmented overhead garage door, have employed a conventional fractional horsepower motor to drive the door between its open and closed positions. The typical segmented overhead-type garage door employs a plurality of rectangular door segments with each segment hinged to an adjacent segment along a horizontally oriented side thereof. An opposed pair of rollers, one mounted on each short vertical side of an individual door segment, are guided and restrained by opposed rails or channels which are securely mounted adjacent the sides of the door opening. The rails or channel-shape members are mounted in an inverted L-shape position with the horizontal top portions thereof extending inwardly into the garage or other structure, preferably being secured to beams or joists therein.
The conventional door opener utilizes a fractional horsepower motor and drives through a gear train to rotate one or more chain sprockets. In turn, a bicycle-type chain which is driven by the sprockets is attached at one distal end thereof to the door, preferably adjacent the top of the door at its center. Driving the fractional horsepower motor in one direction of rotation tends to open the door, and driving it in the opposite direction tends to close the door. Associated electrical circuitry which usually include limit switches turn off the motor when the door reaches a proper open or closed position. While these limit switches could be positioned to be actuated or de-actuated by the movement of the door itself, typically, they are positioned in the housing of the door opener and are tripped by an intermediate member which is mounted for movement inside the housing. This intermediate member is also driven by the fractional horsepower motor. One disadvantage of such a control arrangement is the continuous stretching of the link chain which is being driven by the sprocket and which is directly connected to the door. As the door is opened and closed, the chain stretches and the alignment of the intermediate member with the limit switches does not compensate for the stretching. Therefore, the conventional door opener needs periodic re-adjustment to operate in a satisfactory manner.
Other types of door openers employ pneumatic or hydraulic actuators, conventional motors with associated reduction gears, friction clutches or other power transmitting mechanisms. These door openers are expensive, complex, and difficult to maintain in precise adjustment.
Some linear motor actuators have been utilized to open and close doors which are moved in a single plane, usually to one side of the door opening adjacent which the door is mounted. U.S. Pat. Nos. 1,986,616; 1,986,639; 2,964,260; and 3,374,823 disclose such door openers. These linear motor actuators have typically required three phase power supplies for their use or having utilized sliding contacts or brushes, thus being expensive and complex.